DIC 기법을 통한 산화그래핀 혼입 PVA 섬유보강 시멘트 복합체의 휨거동 특성 분석

조병휘,정성균 한국도로학회 2023 한국도로학회논문집 Vol.25 No.3

PURPOSES : The purpose of this study is to experimentally analyze the flexural strength characteristics of cement mortar mixtures simultaneously incorporated with graphene oxide (GO) and polyvinyl alcohol (PVA) fibers, and to understand the composite effect of those on enhancing resistance against the initiation and progression of micro-cracks, as well as the control of macro-cracks in flexural behavior. METHODS : Cement mortar(w/c=0.5) specimens for flexural strength test, mixing 6 mm and 12 mm PVA fibers at 1% and 2% volume ratios, were fabricated. Additionally, specimens incorporating GO at a cement weight ratio of 0.05% were prepared for each mixture to analyze the effect of GO. Therefore total eight types of mixture were prepared. The fabricated specimens were subjected to flexural strength tests after curing in waterbath for 7 and 28 days. Concurrently, digital images for analyzing deformation in accordance with loading history were obtained at a rate of 20 Hz using the DIC technique. Through displacement and strain calculation via DIC, the flexural behavior characteristics of the mixtures combined with GO and PVA fibers were precisely analyzed. Furthermore, the composite effect on flexural behavior characteristics when GO and PVA fibers are incorporated was discussed. RESULTS : For the PVA fiber-reinforced cement mortar mixture, the incorporation of 0.05% GO increased the crack initiation load by up to 23%, and the maximum resistive load after cracking by up to 24%. Moreover, introducing GO into the PVA fiber-reinforced mixture increased the flexural strain just before cracking by approximately 30 to 50%, while the maximum resistive load after cracking exhibited similar strain levels with or without GO incorporation. Therefore, under flexural behavior, the integration of GO might delay crack initiation by increasing the strain concurrent with the rise in flexural stress before crack occurrence. It also seems to contribute to reducing crack expansion by synergistically interacting with PVA fibers after crack occurrence. CONCLUSIONS : It was experimentally examined that the flexural strength of PVA fiber reinforced cement mortar is improved by incorporating GO. Moreover, GO enhances resistance of crack occurrance and reduces crack propagation in combination with PVA fibers. This study suggests that simultaneous incorporation of GO and PVA fibers can synergistically improve the performance of cement composites.

보강섬유의 형상과 물성에 따른 인발특성이 콘크리트의 휨거동에 미치는 영향

김홍섭,남정수,김정현,한상휴,김규용 한국구조물진단유지관리공학회 2014 한국구조물진단유지관리공학회 논문집 Vol.18 No.5

본 연구에서는 섬유종류에 따른 인발특성과 섬유보강 콘크리트의 휨특성에 대하여 평가하기 위하여, 섬유의 재질 및 형상 다른 후크형강섬유, 비정질 강섬유 및 폴리아미드 섬유에 대하여 인발시험과 섬유보강 콘크리트 시험체를 제작하여 휨특성을 평가하였다. 그 결과, 후크형 강섬유의 경우 최대인발하중에서 섬유가 매트릭스로부터 인발되었지만, 비정질 강섬유는 섬유와 매트릭스의 부착강도가 섬유자체의인장강도보다 높아 섬유가 매트릭스로부터 인발되지 않고 파괴되는 현상을 나타내었다, 한편, 폴리아미드 섬유는 연신율에 의해 최대인발하중까지 변위가 크게 발생하였으며, 최대하중이후에 섬유가 끊어지는 파괴특성을 나타내었다. 섬유보강 콘크리트의 휨특성에 있어서 비정질 강섬유는 매트릭스와의 부착강도가 높고, 섬유의 혼입개체수가 많아 콘크리트의 최대휨강도는 높았지만, 균열발생 이후 섬유가 매트릭스로부터 인발되지 않고 섬유가 파괴되는 것에 의해 응력의 저하가 급격하게 발생하지만, 후크형 강섬유보강 콘크리트는 균열발생 이후 섬유가 인발되면서 응력의 저하가 완만하게 발생하였다. 폴리아미드 섬유보강 콘크리트는 균열발생이후 섬유의 연신률에 의해 응력이 급격하게 저하하는 구간이 발생하였으며, 섬유와 매트릭스의 부착에 의해 재상승하였다가 섬유가 끊어지면서 파괴되었다. 섬유와 매트릭스의 인발특성은 섬유보강 콘크리트의 휨강도 및 변형 능력에 큰 영향을 미치는 것으로 판단된다. This study evaluated the bonding property of fiber and flexural behavior of fiber reinforced concrete. Amorphous steel fiber, hooked steel fiber and polyamide fiber was used for evaluation of bonding property and flexural behavior. As a result, the hookedsteel fiber was pulled out from matrix when peak stress. However amorphous steel fiber occurred shear failure because bondingstrength between fiber and matrix was higher than tensile strength of fiber. Polyamide fibers occurred significantly displacement to peak stress because of elongation of fiber. After that peak stress, fiber was cut off. Amorphous steel fiber reinforced concrete had a greater maximum flexural load compared with hooked steel fiber reinforced concrete because bonding performance between fiber and matrix was high and mixed population of fiber was many. However flexural stress was rapidly reduced in load-deflection curve because of shear failure of fiber. Flexural stress of hooked steel fiber reinforced concrete was slowly reduced because fiber was pulled out from the matrix. In the case of polyamide fiber reinforced concrete, flexural stress was rapidly lowered because of elongation of fiber. However flexural stress was increased again because of bonding property between polyamide fiber and matrix.The pull-out properties of the fiber and matrix has effect on the deformation capacity and flexural strength of fiber reinforced concrete.

보강섬유의 형상과 물성에 따른 인발특성이 콘크리트의 휨거동에 미치는 영향

김홍섭,남정수,김정현,한상휴,김규용 한국구조물진단유지관리공학회 2014 한국구조물진단유지관리공학회 논문집 Vol.18 No.5

This study evaluated the bonding property of fiber and flexural behavior of fiber reinforced concrete. Amorphous steel fiber,hooked steel fiber and polyamide fiber was used for evaluation of bonding property and flexural behavior. As a result, the hookedsteel fiber was pulled out from matrix when peak stress. However amorphous steel fiber occurred shear failure because bondingstrength between fiber and matrix was higher than tensile strength of fiber. Polyamide fibers occurred significantly displacement topeak stress because of elongation of fiber. After that peak stress, fiber was cut off. Amorphous steel fiber reinforced concrete hada greater maximum flexural load compared with hooked steel fiber reinforced concrete because bonding performance between fiberand matrix was high and mixed population of fiber was many. However flexural stress was rapidly reduced in load-deflection curvebecause of shear failure of fiber. Flexural stress of hooked steel fiber reinforced concrete was slowly reduced because fiber waspulled out from the matrix. In the case of polyamide fiber reinforced concrete, flexural stress was rapidly lowered because ofelongation of fiber. However flexural stress was increased again because of bonding property between polyamide fiber and matrix. The pull-out properties of the fiber and matrix has effect on the deformation capacity and flexural strength of fiber reinforcedconcrete. 본 연구에서는 섬유종류에 따른 인발특성과 섬유보강 콘크리트의 휨특성에 대하여 평가하기 위하여, 섬유의 재질 및 형상 다른 후크형강섬유, 비정질 강섬유 및 폴리아미드 섬유에 대하여 인발시험과 섬유보강 콘크리트 시험체를 제작하여 휨특성을 평가하였다. 그 결과, 후크형 강섬유의 경우 최대인발하중에서 섬유가 매트릭스로부터 인발되었지만, 비정질 강섬유는 섬유와 매트릭스의 부착강도가 섬유자체의인장강도보다 높아 섬유가 매트릭스로부터 인발되지 않고 파괴되는 현상을 나타내었다, 한편, 폴리아미드 섬유는 연신율에 의해 최대인발하중까지 변위가 크게 발생하였으며, 최대하중이후에 섬유가 끊어지는 파괴특성을 나타내었다. 섬유보강 콘크리트의 휨특성에 있어서 비정질 강섬유는 매트릭스와의 부착강도가 높고, 섬유의 혼입개체수가 많아 콘크리트의 최대휨강도는 높았지만, 균열발생 이후 섬유가 매트릭스로부터 인발되지 않고 섬유가 파괴되는 것에 의해 응력의 저하가 급격하게 발생하지만, 후크형 강섬유보강 콘크리트는 균열발생 이후 섬유가 인발되면서 응력의 저하가 완만하게 발생하였다. 폴리아미드 섬유보강 콘크리트는 균열발생이후 섬유의 연신률에 의해 응력이 급격하게 저하하는 구간이 발생하였으며, 섬유와 매트릭스의 부착에 의해 재상승하였다가 섬유가 끊어지면서 파괴되었다. 섬유와 매트릭스의 인발특성은 섬유보강 콘크리트의 휨강도 및 변형 능력에 큰 영향을 미치는 것으로 판단된다.

The Effects of Steel Fiber and Nano-SiO2 on the Cyclic Flexural Behavior of Reinforced LWAC Beams

Soodeh Akbarpour,Hooshang Dabbagh,Hamidreza Tavakoli 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.10

The dead load and consequently the burden imposed on the structures due to earthquake can be reduced using Lightweight Aggregate Concrete (LWAC). In this study the cyclic flexural performance of LWAC beams is experimentally investigated to assess the influence of nano-SiO2 and steel fibers on the reversal flexural behavior. Tests were carried out on the reinforced LWAC beams with dimensions of 150 × 200 × 1200 mm under alternative cycles of variable displacement amplitudes. The cyclic behavior of these members including hysteresis response, load bearing capacity, envelope curve, stiffness, energy dissipation capacity and crack pattern are discussed and compared. The results showed that the addition of steel fiber significantly enhanced maximum flexural strength, cumulative dissipated energy, post-cracking stiffness and damage tolerance ability of LWAC beam. Adding nano-silica alone had slight effect on improving the reversal cyclic flexural behavior of LWAC. Furthermore the use of nano-silica increased the effectiveness of steel fiber on enhancement the cyclic flexural performance, especially at higher levels of displacement.

조관에 의한 잔류 응력을 고려한 스파이럴 강관의 휨 거동 분석

김규원,김정수,강동윤,김문겸 한국가스학회 2019 한국가스학회지 Vol.23 No.4

A spiral steel pipe has been more used widely as a structural member as well as transport pipeline because the pipe can be manufactured continuously, consequently more economical than the conventional UOE pipe. As improved pipe manufacture technology makes spiral pipes to have high strength and to have larger diameters, the spiral pipes have been recently used as long distance transport pipeline with a large diameter and strain-based design is thus required to keep structural integrity and cost effectiveness of the spiral pipe. However, design codes of spiral pipe have not been completely established yet, and structural behaviors of a spiral pipe are not clearly understood for strain-based design. In this paper, the effects of residual stresses due to the spiral pipe manufacture process are investigated on the flexural behavior of the spiral pipe. Finite element analyses were conducted to estimate residual stresses due to the manufacturing process for the pipes which have different forming angle, thickness, and strength, respectively. After that, the results were used as initial conditions for flexural analysis of the pipe to numerically investigate its flexural behaviors. 스파이럴 강관은 기존 UOE 강관에 비해 경제적이며 연속적으로 강관 제작이 가능해 수송관뿐만 아니라 구조부재로 사용이 점차 확장되고 있다. 최근 제작기술의 발달로 스파이럴 강관의 고강도 및 대형화가 가능하게 됨에 따라대규모 장거리 수송용 파이프라인에도 적용이 시도되고 있고, 이로 인해 스파이럴 강관의 구조적 건전성과 경제성확보를 위한 변형률 기반 설계가 요구된다. 그러나 이를 뒷받침하기 위한 스파이럴 강관의 설계 기준 전반이 제시되지 않은 실정이고, 구조적 거동에 대한 명확한 규명이 이뤄지지 못하고 있다. 본 논문은 스파이럴 파이프의 조관과정에서 발생되는 잔류응력이 스파이럴 파이프의 휨 거동에 미치는 영향을 분석하였다. 조관으로 인한 잔류응력평가를 위해 조관 성형각, 두께, 강도를 달리하여 스파이럴 파이프의 유한요소해석을 수행하고, 해석결과를 파이프 휨 해석에 대한 초기 조건으로 반영하여 수치해석적으로 휨 거동 변화를 조사하였다.

티타늄 금속봉으로 보강된 화강암의 휨거동

하태욱(Ha, Tae-Uk),홍성걸(Hong, Sung-Gul),임우영(Lim, Woo-Young) 대한건축학회 2019 大韓建築學會論文集 : 構造系 Vol.35 No.4

In this study, flexural tests of granite reinforced with titanium metal rods were carried out to repair and restore the damaged stone-made cultural heritage, the Stone Pagoda of the Mireuksa Temple Site. A total of twelve specimens were tested. The primary test parameters are the reinforcement ratio and the location of the reinforcement. For restoration, epoxy resin was used for joining the separated stones, and titanium metal rods were used for structural reinforcement. Test results showed that the flexural failure took place in specimens with a reinforcement ratio of 0.8% or less, and shear failure occurred when the reinforcement ratio was 1.68% or more. The peak load of the reinforced stone was found to be highly related to the reinforcement ratio. The peak load increased with increasing the reinforcement ratio. Also, the flexural behaviors of the reinforced stones were affected by the location of the reinforcement. Based on the test results, this study recommends the reinforcement ratio of the reinforced granite to induce ductile behavior.

비소성 시멘트 콘크리트의 휨 거동에 관한 연구

유성원,남은용,이상준,황선복,소양섭,김재신 한국안전학회 2012 한국안전학회지 Vol.27 No.2

If cement can be manufactured with industrial byproducts such as granulated blast furnace slag,phosphogypsum, and waste lime instead of clinker, there would be many advantages, including maximum use of these industrial byproducts for high value-added resources, conservation of natural resources and energy by omitting the use of clinker, minimized environmental pollution problems caused by CO2 discharge, and reduction of the production cost. By this reason, in this study, mechanical behavior tests of non-burnt cement concrete were performed, and elasticity modulus and stress-strain relationship of non-burnt cement concrete were proposed. 6 test members were manufactured and tested according to reinforcement ratio and concrete compressive strength. By the test results, there was no difference between ordinary concrete and non-burnt cement concrete of flexural behavior. In order to verify the proposed non-burnt cement concrete model, nonlinear analytical model was derived by using strain compatibility method. By the results of comparison between test results, ordinary concrete model and proposed model, The proposed model well predicted the flexural behavior of non-burnt cement concrete

150㎫ 초고강도 철근콘크리트 보의 휨거동에 관한 실험적 연구

김도우(Kim Do-Woo),강훈(Kang Hoon),안종문(Ahn Jong-Mun),신성우(Shin Sung-Woo) 대한건축학회 2009 대한건축학회 학술발표대회 논문집 - 계획계/구조계 Vol.29 No.1(구조계)

An evaluate on structural behavior of ultra high strength concrete(UHSC) is necessary and important, because that is different from normal strength concrete. And it is important to evaluate on serviceability of RC structure which is used ultra high strength concrete. The reinforced ultra-high-strength-concrete beam subjected to flexural moment behaves more brittleness than the moderate strength concrete beam reinforced with equal reinforcement ratio(ρ/ρb, ρb=balanced steel ratio). In this study, 10 singly reinforced rectangular beam specimens used 150 ㎫ concrete compressive strength were tested to evaluate on flexural behavior. Test results show that when the concrete compressive strength with 150㎫, the maximum reinforcement ratio should be less than 0.625ρb for ductile behavior. And the shape of the compressive stress block is expected to triangle.

외부 부분 부착 PSC 보의 휨거동 실험

유성원 ( Sung Won Yoo ),이상준 ( Sang Jun Lee ) 한국안전학회(구 한국산업안전학회) 2012 한국안전학회지 Vol.27 No.5

Recently, the external prestressed concrete structures are increasingly being built. The mechanical behavior of prestressed concrete beams with external tendon is different from that of normal bonded PSC beams in that the increment of tendon stress was derived by whole member behavior. By this reason, the ultimate stress of external tendon is smaller than that of bonded tendon or internal unbonded tendon. The purposes of the present paper are therefore to improve the mechanical behavior of external unbonded tendon by using partially bonded external tendon and to evaluate the flexural behavior of partially bonded external tendon by the flexural member experiment. From the experimental results, before flexural cracking, there was no difference between external unbonded, partially bonded and bonded tendons. However, after cracking, yielding load of reinforcement, ultimate load, and tendon stress were increased in the sequence of external unbonded, partially bonded and bonded tendon members. The equation of ACI-318 and AASHTO 1994 were not matched with test results and had no correlations. So the newly proposed equation will be needed including the consideration of tendon profile, tendon bonded type, and so on. The proposed partially bonded external tendon in this paper will be a effective basis for the evaluation of external tendons in construction and design.

목차 : 비소성 시메트 콘크리트의 휨 거동에 관한 연구

유성원 ( S W Yoo ),남은용 ( E Y Nam ),이상준 ( S J Lee ),황선복 ( S B Hwang ),소양섭 ( Y S Soh ),김재신 ( J S Kim ) 한국안전학회(구-한국산업안전학회) 2012 한국안전학회지 Vol.27 No.2

If cement can be manufactured with industrial byproducts such as granulated blast furnace slag, phosphogypsum, and waste lime instead of clinker, there would be many advantages, including maximum use of these industrial byproducts for high value-added resources, conservation of natural resources and energy by omitting the use of clinker, minimized environmental pollution problems caused by C02 discharge, and reduction of the production cost. By this reason, in this study, mechanical behavior tests of non-burnt cement concrete were performed, and elasticity modulus and stress-strain relationship of non-burnt cement concrete were proposed. 6 test members were manufactured and tested according to reinforcement ratio and concrete compressive strength. By the test results, there was no difference between ordinary concrete and non-burnt cement concrete of flexural behavior. [n order to verif5, the proposed non-burnt cement concrete model, nonlinear analytical model was derived by using strain compatibility method By the results of comparison between test results, ordinary concrete model and proposed model, The proposed model well predicted the flexural behavior of non-burnt cement concrete.